The invention relates to a configuration having two amplifiers configured such that selectively only one of the amplifiers is intended to provide an amplification.
In existing configurations of this type, the changeover from the first amplifier to the second amplifier, or vice versa is effected using changeover devices of varying complexity. Occasionally, such a changeover device has a relatively complicated construction and, moreover, requires at least one additional (control) terminal, which may be disadvantageous in particular in the case of integrated circuits or when accommodating the configuration in a miniature housing; in particular, the required chip area and the RF properties may be adversely affected as a result.
Published British Patent Application No. GB 2 289 810 A discloses a switching device for RF signals, in which bipolar amplifier transistors are coupled to a single output at their collector and are driven by a respective RF signal at their base. For the purpose of changing over between the transistors, a control device is provided which, depending on a control signal fed to its input, generates on the output side respective switching signals which are assigned to the amplifier transistors and are coupled in at their base terminals.
Published European Patent Application No. EP 0 648 010 A discloses a differential amplifier with two emitter-coupled amplifier transistors which are connected to a supply potential terminal via a current source. Two further emitter-coupled transistors, which are connected to the supply potential terminal via a separate current source, are connected, on the one hand, by their base to the base terminals of the first-mentioned transistors and, on the other hand, by their collector in a cross-coupled manner to the base terminals of the first-mentioned transistors.
U.S. Pat. No. 4,417,240 disclose measures for generating bias voltages that are to be applied to input terminals of amplifier transistors.
It is accordingly an object of the invention to provide a circuit configuration which overcomes the above-mentioned disadvantages of the heretofore-known configurations of this general type and which allows to effect the changeover between the amplifiers with minimal additional outlay and without any disturbances.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration, including:
a first amplifier having a first controlled path connected to ground and a first terminal for receiving a signal to be amplified;
a second amplifier having a second controlled path connected to ground and a second terminal for receiving a signal to be amplified; and
a switching element having a switched path with a first side connected to ground and with a second side connected to one of the first and second terminals, the switched path of the switching element being configured to be controllable by a signal present at another one of the first and second terminals.
It is provided that the second amplifier is operated depending on the conditions established at the input terminal of the first amplifier, in that a switching element connected to the signal input of one of the amplifiers is switchable in a manner dependent on a signal that is present at the signal input of the other amplifier.
If the conditions depending on which the second amplifier is operated are considered to be only those conditions which do not exhibit any interactions with the signals that are to be amplified by the first amplifier, that is to say, for example, the DC voltage established at the input terminal of the first amplifier, if the signal to be amplified is an RF signal, then the changeover between the amplifiers can be controlled via the input terminal of the first amplifier. Such a changeover can be realized extremely simply and, precisely because of this simplicity, can be effected without any problems and without any effects, or at any rate without any appreciable effects, on the function and mode of operation of the amplifiers.
According to another feature of the invention, the second amplifier is configured to be operated in dependence on a voltage level and/or a voltage profile established at the first terminal of the first amplifier.
According to yet another feature of the invention, the first and second amplifiers are configured to amplify analog AC voltages, and the second amplifier is configured to be operated in dependence on a DC voltage level established at the first terminal of the first amplifier.
According to a further feature of the invention, the first and second amplifiers are configured such that a DC voltage established at the second terminal of the second amplifier is varied depending on the DC voltage level established at the first terminal of the first amplifier.
According to another feature of the invention, a DC voltage generating circuit is connected to the first terminal of the first amplifier and to the second terminal of the second amplifier for providing DC voltages to the first and second terminals.
According to yet another feature of the invention, the DC voltage generating circuit generates the DC voltages with given values such that the first and second amplifiers are enabled to amplify signals to be amplified.
According to a further feature of the invention, the first and second amplifiers are configured such that, if a DC voltage established at the first terminal of the first amplifier has a given value at which signals to be amplified by the first amplifier can be amplified, then a DC voltage established at the second terminal of the second amplifier is left at or brought to a value at which the second amplifier is unable to amplify signals to be amplified.
According to yet a further feature of the invention, the first and second amplifiers are configured such that, if a DC voltage established at the first terminal of the first amplifier has a given value at which the first amplifier is unable to amplify signals to be amplified, then a DC voltage established at the second terminal of the second amplifier is left at or brought to a value at which the second amplifier is able to amplify signals to be amplified.
According to another feature of the invention, the first amplifier is configured such that a DC voltage established at the first terminal of the first amplifier is adjustable or variable via the first terminal for receiving signals to be amplified by the first amplifier.
According to another feature of the invention, the first amplifier is a first transistor and the second amplifiers is a second transistor; and the first amplifier has a gate terminal, the second transistor is configured to be operated in dependence of one of a voltage level and a voltage profile established at the gate terminal of the first transistor.
According to a further feature of the invention, the first amplifier is a first transistor and the second amplifiers is a second transistor; each of the first and second transistors has a first gate terminal, a second gate terminal and a controlled path; the first gate terminal of the first transistor forms the first terminal for receiving a signal to be amplified, the first gate terminal of the second transistor forms the second terminal for receiving a signal to be amplified; the second gate terminal is a terminal for setting a gain; further transistors are respectively assigned to the first and second amplifiers; each of the further transistors has a controlled path and two gate terminals; the first and second gate terminals of the first and second transistors are coupled to respective ones of the two gate terminals of the further transistors; and the controlled path of each of the further transistors is connected to ground and coupled to the controlled path of a respectively assigned one of the first and second amplifiers.
According to another feature of the invention, two series circuits are provided, each of the series circuits including two resistors and a node between the two resistors; the first and second terminals of the first and second amplifiers being coupled to respective ones of the two gate terminals of the further transistors via the two series circuits; and the switching element having a control terminal, the switched path of the switching element and the control terminal of the switching element being respectively coupled to the node of a respective one of the two series circuits.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration having a first amplifier and a second amplifier, of which in each case only at most one is intended to effect amplification, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.